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At least 1,639 records · Page 91Linked to original sources
PubMed1999

A phosphoglycerate to inorganic phosphate ratio is the major factor in controlling starch levels in chloroplasts via ADP-glucose pyrophosphorylase regulation.

Purified barley leaf ADP-glucose pyrophosphorylase, a key enzyme of the starch synthesis in the chloroplast stroma, was analysed with respect to its possible regulation by factors defining the metabolic/effector status of the chloroplast during light and dark conditions. The enzyme required 3-phosphoglyceric acid for the maximal activity and was inhibited by inorganic phosphate. The optimal pH for the enzyme was at circa 7.0, regardless of the presence or absence of 3-phosphoglyceric acid, whereas the maximal activation by 3-phosphoglyceric acid was observed at pH 8.5 and higher. Changes in the concentration of Mg2+ and dithiothreitol had little or no effect on the enzymatic activity of AGPase. It has been directly demonstrated for the first time that a 3-phosphoglyceric acid/inorganic phosphate ratio, a crucial regulatory parameter, could be directly related to a defined activation state of the enzyme, allowing the prediction of a relative AGPase activity under given conditions. The predicted changes in the enzyme activity were directly correlated with earlier reported responses of starch levels to the 3-phosphoglyceric acid/inorganic phosphate ratio in chloroplasts. Consequences of this for the starch biosynthesis are discussed.

Chloroplasts↗
PubMed1988

Partitioning behavior of erythrocytes in aqueous two-phase systems containing hydroxypropyl starch and polyethylene glycol.

The partitioning behavior of erythrocytes in Reppal PES 200 (a hydroxypropyl starch produced by Reppe Glykos AB, Växjö, Sweden)-polyethylene glycol (PEG) and in dextran (Dx)-PEG aqueous phase systems made isotonic with phosphate is similar in a number of ways: (i) There is a correlation between the relative electrophoretic mobilities and partition ratios, P, of red blood cells from different species; (ii) The cell P is reduced when, at constant polymer concentrations, phosphate is systematically replaced by sodium chloride (with the total concentration isotonic); (iii) The cell P is increased with reduced polymer concentrations (decreased interfacial tensions); (iv) Treatment of erythrocytes with neuraminidase results in a reduced P value; (v) Rat red cells of different ages can be fractionated by counter-current distribution; and (vi) Differences between red blood cells from genetically distinct rats or between humans can be detected. Aquaphase (a hydroxypropyl starch marketed by Perstorp AB, Lund, Sweden) has been tested as in ii-iv above with analogous results. The partitioning behavior of erythrocytes in PES-PEG and Dx-PEG aqueous phase systems containing sodium chloride differs in a number of ways: (vii) The correlation, apparent in Dx-PEG systems, between the P value of red blood cells from different species and the ratio of their membrane poly- to monounsaturated fatty acids is absent in PES-PEG systems. It is replaced by a correlation as in i; (viii) The increase in P value in Dx-PEG observed from red blood cells after treatment with neuraminidase is replaced by a decrease in P value in PES-PEG or Aquaphase-PEG systems. We conclude that PES (and Aquaphase) can be substitutes for dextran in cell partitioning studies when charge-sensitive phases are used (e.g., those containing phosphate) while separations based on properties reflected by Dx-PEG systems containing sodium chloride are not duplicated by PES-PEG (and probably not by Aquaphase-PEG). The hydroxypropyl starch-PEG systems containing sodium chloride, unlike the analogous Dx-PEG systems, have a significant electrostatic potential difference between the phases.

Aging↗
PubMed2003

Increased butyrate formation in the pig colon by feeding raw potato starch leads to a reduction of colonocyte apoptosis and a shift to the stem cell compartment.

Whereas butyrate is well known to induce apoptosis in transformed colon cells in vitro, evidence exists that it inhibits apoptosis of colon crypt cells in vivo. In this study, pigs were fed with resistant potato starch to increase microbial butyrate formation in the colon and to investigate its effects on mitosis and apoptosis. In addition, apoptosis regulating proteins were determined by immunocytochemistry, such as proapoptotic Bak, antiapoptotic Bcl-2, and the epidermal growth factor (EGF), which is synthesized by goblet cells and functions as a survival factor. Two groups of 6 barrows were both supplied with 381 g crude protein and 31 MJ metabolizable energy (ME) daily over a 19-day experimental period. The rations differed in the carbohydrate composition. The controls received gelatinized starch as the main carbohydrate, whereas the experimental group (butyrate group) received a ration with raw potato starch (low ileal digestibility). In the feces, butyrate concentration and pH were monitored daily. After killing the pigs, colon tissue was obtained for histologic and immunocytochemical evaluation, which was performed separately in the luminal, middle, and stem cell compartment of the crypts. In the butyrate group, the total number of apoptotic cells was reduced by 34% (P< or =.001) compared with controls, whereas the mitotic rate was not altered. The crypt depth was only moderately increased by 15%. Apoptosis in the luminal compartment of the butyrate group was reduced by 18.8%, but was increased by 21.7% in the stem cell compartment. The effect of butyrate on apoptosis was paralleled by an increased number of Bcl-2 positive cells mainly in the luminal compartment (butyrate: 2.6 cells; controls: 1.2 cells, P< or =.001), which was more pronounced compared with the number of Bak positive cells in the same compartment. Bak activity in the stem cell compartment was 3.4-fold increased compared with controls (P< or =.001). The size of EGF-positive stained mucus-droplets from the goblet cells was increased in the butyrate group (P< or =.001). We conclude that butyrate inhibits apoptosis of colonocytes in vivo. An excessive proliferation of crypts is counteracted by a shift of the remaining apoptosis towards the stem cell compartment.

Animals↗
PubMed1999

Effects of red wine, tannic acid, or ethanol on glucose tolerance in non-insulin-dependent diabetic patients and on starch digestibility in vitro.

This study examines the effect of moderate intake of red wine, tannic acid, or ethanol during a meal in type 2 diabetic patients and the influence of tannic acid on the digestibility of starch by alpha-amylase. Thirty non-insulin-dependent diabetes mellitus (NIDDM) patients aged 53 +/- 6 years were studied (in vivo study) 10 of whom received red wine (200 mL), 10 tannic acid (150 mg), and 10 ethanol (16 g) with their midday meal (600 calories, 65 g carbohydrate, 20 g lipid, and 34 g protein). All patients were tested on two occasions (water or placebo v wine, alcohol, or tannic acid). The influence of tannic acid (0.25, 0.5, and 1 mg) on the digestibility of starch (100 mg) by alpha-amylase (100 U) was tested in vitro by sequential incubation at 37 degrees C (in vitro study). The maximum glucose excursion after lunch was 2.6 +/- 0.8 mmol/L at 90 minutes (T90) for water and 1.8 +/- 0.9 mmol/L at T90 for red wine taken with the meal. The values at T60 and T90 were significant (P < .01). Comparable results were obtained with tannic acid alone (nonalcoholic component of wine): the maximum glucose excursion after lunch was 2.76 +/- 0.9 mmol/L at T120 for placebo and 1.97 +/- 0.9 mmol/L at T90 for tannic acid (P < .01); no difference in glucose and insulin excursion was observed between water and ethanol. No interaction between tannic acid and starch was observed in the in vitro experiments, although after preincubation of alpha-amylase with tannic acid, digestion was slowed in a dose-dependent manner (6.1 +/- 1.1 minutes for 0.25 mg tannic acid and 13.1 +/- 1.59 minutes for 1 mg tannic acid). Drinking red wine with a meal did not increase blood glucose in NIDDM patients, and led to a slight decrease in some instances. The effect appeared to be mediated by the nonalcoholic compounds in wine such as tannic acid. Ethanol itself had no effect on plasma glucose or insulin levels.

Blood Glucose↗
PubMed2003

Effect of high temperature on fine structure of amylopectin in rice endosperm by reducing the activity of the starch branching enzyme.

Rice (Oryza sativa L.) grain quality is affected by the environmental temperature it experiences. To investigate the physiological molecular mechanisms of the effect of high temperatures on rice grain, a non-waxy indica rice was grown under two temperature conditions, (29/35 degrees C) and (22/28 degrees C), during the ripening stage in two phytotrons. The activities and gene expression of key enzymes for the biosynthesis of amylose and amylopectin were examined. The activity and expression levels of soluble endosperm starch synthase I were higher at 29/35 degrees C than that at 22/28 degrees C. In contrast, the activities and expression levels of the rice branching enzyme1, the branching enzyme3 and the granule bound starch synthase of the endosperm were lower at 29/35 degrees C than those at 22/28 degrees C. These results suggest that the decreased activity of starch branching enzyme reduces the branching frequency of the branches of amylopectin, which results in the increased amount of long chains of amylopectin of endosperm in rice grain at high temperature.

1,4-alpha-Glucan Branching Enzyme↗
PubMed2003

Synthesis of starch derivatives with labile cationic groups.

A new route to starch derivatives bearing hydrolyzable cationic groups was developed. This was based on reacting starch compounds with betaine derivatives in the presence of diisopropylcarbodiimide and 4-dimethylaminopyridine as coupling reagents in an aprotic polar solvent. Water-soluble starches with a perfectly controlled degree of substitution were thus obtained which were fully characterized by infrared, 1H and 13C spectroscopy and viscosity measurements. The cationic groups grafted on the polysaccharides are shown to hydrolyze slowly upon storage at room temperature.

4-Aminopyridine↗
PubMed1997

Influence of growth conditions on barley starch properties.

Air equilibrated barley starch comprises amylopectin, amylose, lipid and water. The structure of amylose and amylopectin, and the proportion of amylose in granules is under genetic control and is therefore subject to genotypic variation. The amount of lipid (which is essentially all lysophospholipid) is similarly under genetic control. Environment and especially environmental temperature do, however, have a regulatory effect on the size of starch granules, the amylose to amylopectin ratio and the amount of lipid (which is essentially all complexed with amylose) within barley starch. High growth temperatures probably facilitate amylopectin crystallisation and increase gelatinisation temperatures, (and to some extent the enthalpy of gelatinisation), but delay the onset and depress the extent of swelling of granules when heated in water.

Food Technology↗
PubMed1997

Enzymic analysis of the structure of oxidized potato starches.

The possibility to use enzymic methods for the analysis of the positions of carboxyl and carbonyl groups in sodium hypochlorite oxidized (HO) and hydrogen peroxide oxidized (PO) potato starches was investigated. The HO-starch, that contained more modified glucosyl residues, possessed a lower beta-amylolysis limit and all of the polymer components were resistant to complete hydrolysis as judged from gel-permeation chromatograms. In contrast, the PO-starch contained 24% of apparently unmodified, linear chains that were hydrolysed by beta-amylase. After debranching, approximately 30% of the chains in the HO-sample and approximately 20% in the PO-sample remained partly resistant to successive beta-amylolysis.

Amylopectin↗
PubMed2000

Annealing of starch - a review.

Annealing processes, involving specific heating protocols, have been used by man for centuries to impart desirable properties to materials - especially metals and particularly tools and weapons. The terminology has also been applied to biopolymers such as starches, where the effects of the processing have been known for decades although the molecular basis has not been at all well understood. Because of the marked effect the annealing process has on starch functionality and consequently industrial applications, it is critical that the underlying molecular events are understood. This review is an attempt to clarify the process of starch annealing with an emphasis on data generated in the authors' laboratory.

Gelatin↗
PubMed2003

Engineering cyclodextrin glycosyltransferase into a starch hydrolase with a high exo-specificity.

Cyclodextrin glycosyltransferase (CGTase) enzymes from various bacteria catalyze the formation of cyclodextrins from starch. The Bacillus stearothermophilus maltogenic alpha-amylase (G2-amylase is structurally very similar to CGTases, but converts starch into maltose. Comparison of the three-dimensional structures revealed two large differences in the substrate binding clefts. (i) The loop forming acceptor subsite +3 had a different conformation, providing the G2-amylase with more space at acceptor subsite +3, and (ii) the G2-amylase contained a five-residue amino acid insertion that hampers substrate binding at the donor subsites -3/-4 (Biochemistry, 38 (1999) 8385). In an attempt to change CGTase into an enzyme with the reaction and product specificity of the G2-amylase, which is used in the bakery industry, these differences were introduced into Thermoanerobacterium thermosulfurigenes CGTase. The loop forming acceptor subsite +3 was exchanged, which strongly reduced the cyclization activity, however, the product specificity was hardly altered. The five-residue insertion at the donor subsites drastically decreased the cyclization activity of CGTase to the extent that hydrolysis had become the main activity of enzyme. Moreover, this mutant produces linear products of variable sizes with a preference for maltose and had a strongly increased exo-specificity. Thus, CGTase can be changed into a starch hydrolase with a high exo-specificity by hampering substrate binding at the remote donor substrate binding subsites.

Binding Sites↗
PubMed1998

Effects of mutations in the starch-binding domain of Bacillus macerans cyclodextrin glycosyltransferase.

Cyclodextrin glycosyltransferase (CGTase) is an industrially important enzyme that produces cyclodextrins (CD) from starch by intramolecular transglycosylation. CGTase consists of five globular domains labeled A through E. To better understand the role of domain E in CGTase catalysis, we have constructed several mutants of Bacillus macerans CGTase. Removing the entire E domain resulted in an inactive enzyme. Adding six amino acids between domains D and E caused a decrease in activity and thermostability. Replacing domain E with the similar starch-binding domain from Aspergillus awamori glucoamylase I caused a drastic decrease in activity, indicating the necessity of correct alignment of bound substrate. Substituting tyrosine residue 634 (Tyr634) with phenylalanine had very little effect on activity or thermostability. Substituting Tyr634 with glycine resulted in a 25% increase of specific cyclization and starch-hydrolyzing activities compared with that of the wild-type enzyme. The latter mutant was less thermostable. The results of this study indicate that domain E is important for the stability and integrity of B. macerans CGTase.

Bacillus↗
PubMed2002

Polyacryl starch microparticles as adjuvant in oral immunisation, inducing mucosal and systemic immune responses in mice.

A new vaccine adjuvant for oral administration has been examined in mice. Polyacryl starch microparticles (2-3 microm in diameter) are prepared from a water-in oil-emulsion with stabilising hydrocarbon chains. A model antigen, human serum albumin (HSA), which is not binding to the gut epithelium, was covalently coupled to the highly porous starch particles. Upon oral administration, the HSA-microparticles induced a good, diversified immune response without any signs of tolerance development. A strong cellular response can be detected as a delayed-type hypersensitivity reaction. The Th1/Th2 ratio increased with the number of doses and time during the immunisation procedure as indicated by the subclass distribution of the systemic, humoral response. Furthermore, the mucosal response was very strong in the groups that received HSA-microparticles, while the groups receiving soluble HSA did not have any detectable s-IgA in faeces. The specificity was confirmed in an ELISPOT assay. These findings indicate that starch microparticles can be an interesting candidate as an oral vaccine adjuvant. The possible causes of the strong immune responses and the possible role of the dendritic cells in the diversified immune response are discussed.

Adjuvants, Immunologic↗
PubMed2001

Sedimentable amyloplasts in starch sheath cells of woody stems of Japanese cherry.

We examined whether sedimentable amyloplasts act as statolith in the perception of gravity in woody stems using the elongated internodes of Japanese cherry (Prunus jamasakura Sieb. ex Koidz.). In the internode of the seedlings grown on earth, amyloplasts were found sedimented at the distal end of each cell of the endodermal starch sheath tissue. In the internode grown on three-dimensional (3-D) clinostat, amyloplasts were dispersed throughout the cell matrix in the endodermal starch sheath tissue. After changing the positions of the internode from vertical to horizontal, re-sedimentation of amyloplasts toward the direction of gravity was completed in 1h, whereas the bending of the internode was observed after 12 days. We propose that sedimentable amyloplasts in the endodermal starch sheath cells may play a role in gravity perception leading to secondary xylem formation in the secondary thickening growth and eccentric growth in gravi-bending of tree stems.

Gravitation↗
PubMed2003

Biohydrogen production from starch in wastewater under thermophilic condition.

Batch experiments were conducted to convert starch in wastewater into hydrogen at 55 degrees C at various wastewater pH (4.0-9.0) and starch concentrations (9.2-36.6 g/l). The maximum hydrogen yield of 92 ml/g of starch added (17% of the theoretical value) was found at wastewater pH 6.0, and the maximum specific hydrogen production rate of 365 ml/(g-VSS.d) was at wastewater pH 7.0. The methane-free biogas contained up to 60% of hydrogen. The mixed liquor was composed mostly of acetate (40.2-53.4%) and butyrate (26.0-40.9%). Phylogenetic analysis based on 16S rDNA sequences of the 72 clones developed from the sludge at pH 6.0 shows that 85.7% of the clones were closely affiliated with genus Thermoanaerobacterium in family Thermoanaerobacteriaceae; the remaining 14.3% were with an uncultured Saccharococcus sp. clone ETV-T2.

Bacteria↗
PubMed1998

Cutinase purification on poly(ethylene glycol)-hydroxypropyl starch aqueous two-phase systems.

The partition behaviour of cutinase on poly(ethylene glycol) (PEG)-hydroxypropyl starch aqueous two-phase systems was characterized. The effect of molecular mass of PEG, the pH of the system and tie-line length on cutinase partition coefficient and cutinase yield to the top phase was investigated for systems prepared with a purified hydroxypropyl starch (Reppal PES 100) and a crude one (HPS). The effect of the presence of different salts, such as sodium chloride, sodium sulphate and ammonium sulphate, on cutinase partition was also studied. The results lead to the conclusion that aqueous two-phase systems composed of PEG and hydroxypropyl starch are not efficient in the purification of cutinase. In the majority of cases, the partition coefficients were very close to 1, with pH being the factor which affects most cutinase partition. Partition coefficients were significantly improved when salts were added to the systems. For PEG 4000-Reppal PES 100 [at pH 4.0; 0.5 M (NH4)2SO4], the partition coefficient for cutinase was 3.7, while a value of 12 was obtained for PEG 4000-HPS (at pH 4.0; 1 M NaCl). An isoelectric point (pI) of 7.8 was confirmed for cutinase by constructing a cross partition graphic from the results obtained in the experiments with different salts.

Carboxylic Ester Hydrolases↗
PubMed2001

Influence of hydrogel structure on the processes of water penetration and drug release from mixed hydroxypropylmethyl cellulose/thermally pregelatinized waxy maize starch hydrophilic matrices.

The kinetics of water penetration and molsidomine release from both hydroxypropylmethyl cellulose (HPMC) and mixed HPMC/thermally pregelatinized waxy maize starch (SDWMT) hydrophilic matrices has been examined in 0.1 mol x dm(-3) HCl (pH 1.0) and 0.06 mol x dm(-3) Na3PO4/HCl buffer (pH 6.8). The rheological oscillatory test parameters of their gel layers obtained by swelling of the matrices in the two aqueous media have been observed. The kinetic swelling properties of mixed HPMC/SDWMT hydrogels (i.e. degree and velocity of both water penetration and swelling, transport mechanism which controls solvent sorption) directly influence the drug release behaviour and the structural features of the formed gel layer. Both diffusion processes are diffusion-controlled ones, their mechanisms being influenced insignificantly by the relaxation properties of the hydrated macromolecules. It has been established by means of comparative viscoelastic analysis, that mixed HPMC/SDWMT hydrogels demonstrate the typical behaviour of 'filled' composite systems having poor adhesion between the surface of the elastic SDWMT 'filler' and the continuous HPMC phase. Due to the inter-phase relations between the swollen starch granules and the linear cellulose derivative as well as to the specific structure of amylopectin molecule, the pregelatinized waxy maize starch shows a stronger influence on the velocities of both water penetration and drug release from mixed HPMC/SDWMT matrices.

Hydrogels↗
PubMed2000

Molecular diversity of lactic acid bacteria from cassava sour starch (Colombia).

Lactic acid bacteria and more particularly lactobacilli and Leuconostoc, are widely found in a wide variety of traditional fermented foods of tropical countries, made with cereals, tubers, meat or fish. These products represent a source of bacterial diversity that cannot be accurately analysed using classical phenotypic and biochemical tests. In the present work, the identification and the molecular diversity of lactic acid bacteria isolated from cassava sour starch fermentation were assessed by using a combination of complementary molecular methods: Randomly Amplified Polymorphic DNA fingerprinting (RAPD), plasmid profiling, hybridization using rRNA phylogenetic probes and partial 16S rDNA sequencing. The results revealed a large diversity of bacterial species (Lb. manihotivorans, Lb. plantarum, Lb. casei, Lb. hilgardii, Lb. buchneri, Lb. fermentum, Ln. mesenteroides and Pediococcus sp.). However, the most frequently isolated species were Lb. plantarum and Lb. manihotivorans. The RAPD analysis revealed a large molecular diversity between Lb. manihotivorans or Lb. plantarum strains. These results, observed on a rather limited number of samples, reveal that significant bacterial diversity is generated in traditional cassava sour starch fermentations. We propose that the presence of the amylolytic Lb. manihotivorans strains could have a role in sour starch processing.

DNA, Ribosomal↗
PubMed2000

Effects of micronutrients on growth and starch hydrolysis of Thermococcus guaymasensis and Thermococcus aggregans.

The effects of micronutrients on growth of Thermococcus guaymasensis and Thenrmococcus aggregans in a starch-containing medium were investigated. A trace minerals solution, a vitamins solution and calcium chloride were omitted from the medium or added in different amounts. The growth rates of both species were not affected over a significant range of concentrations of these compounds, but appreciable inhibition of growth was observed after the addition of elemental sulfur to the medium. T. guaymasensis exhibited a significant tolerance to high amounts of trace element and vitamin solutions but growth was inhibited by the omission of these compounds from the medium. Moreover, both amylolytic and pullulytic activities increased in the presence of 6-fold higher amounts of trace element and vitamin solutions, compared to the concentrations used in the usual medium. In T. aggregans, both enzymatic activities were enhanced in the presence of either increased (4-fold) amounts of trace element and vitamin solutions, or after the addition of elemental sulfur to the medium. Furthermore, larger activities of starch-hydrolysing enzymes were detected with a 10-fold higher concentration of calcium chloride, compared to the usual medium, in the absence of trace element and vitamin solutions. When both Thermococcus species were tested for the tolerance to specific cations and oxyanions, T. guaymasensis exhibited higher tolerance compared to T. aggregans, the former strain being capable to grow in the presence of 6 mM Ni2+, 4mM Cu2+, 1.5 mM SeO4(2-), and 1.5 mM MoO4(2-). The content of total cell proteins followed the pattern of starch-hydrolysing enzymes and an over-expression of proteins in the range of 35, 50 and 70 kDa was observed.

Culture Media↗